Stabilization of ammonium carbamate for fertilizer use



United States Patent 3,314,779 STABILIZATION OF AMMONIUM CARBAMATE FOR FERTILIZER USE Archie V. Slack, Sheffield, Ala., assignor toTennessee Valley Authority, a corporation of the UnitedStates N0 Drawing. Filed May 5, 1964, Ser. No. 365,214 6 Claims. (Cl. 7 30) The invention herein described may be manufactured and used by or for the Government for governmental mally volatile solid, material.

Ammonium carbamate nearly 36 anhydrous having a nitrogen content of percent is easily prepared by the reaction of recycling facilities are needed in the preparation of ammonium carbamate, as is required in the production of urea.

Heretofore, however, the chemical uies and the subsequent storage of same in containers, the walls of which are substantially impervious to ammonia vapors.

I have overcome the difiiculties inherent in the processes of the inexpensive petroleum oil of medium viscosity; and bagging the product for storage or shipment in medium weight In another form 3,314,779 Patented Apr. 18, 1967 Among these advantageous features are: the preparation of a fertilizer material of relatively high nitrogen content (36 percent N),

thereby eliminating the necessity of any drying operation prior to bagging the fertilixer material. In

altered, carbamate as a fertilizer material.

Another object of the present invention is to provide losses during its manufacture, tion.

that this more detailed description is given by Way of illustration and explanation only, and not by way since various changes therein may be made A dry solid is produced directly in the dryfilm reactor.

Following recovery of the precipitated carbamate is the compaction, or pelletizing, step. Any of the commercial pelletizing methods might serve, but pressure compaction appears to be the most suitable. It has been treatment. equipment offers the most economical method of pelletizing, but tabletting is equally elfective. Non pressure compaction (granulation) might the pellets are Tests have significantly for smaller would therefore be desirable to produce and screen for product the largest particles possible, conbe hooded for minimum processing losses.

.tolerable amount.

two inches, should be adequate.

contain fertilizers is well known;

material by coating and increasing sistent with optimum pelletization and recycling costs and with customer acceptability.

The final treatment of the screened carbamate is the coating step. Any medium viscosity oil (about 2.15 Saybolt seconds at 130 F.; equivalent to SAE30) was found to be effective in reducing decomposition of the carbamate to 2 to 3 percent in tfive hours when about 4 to 5 percent of oil was sprayed on the pellets. A mixture of No. 6 fuel oil (77 percent) and No. 1 diesel oil (23 percent) was quite effective and was a relatively low cost combination. A cost of about $0.80 per ton of coated product was estimated for this mixed oil. The oil may be applied easily by spraying onto a rolling bed of pellets in a rotary drum; pressure spray nozzles or air-atomizing sprays may be used. Any other type of uniform application would be effective.

While petroleum oil coatings have been found to be the least expensive and easiest coatings to apply to carbeen found to be of decomposition.

of coating have reducing the rate bamate, other types equally effective in Pellets first impregnated with oil (23 percent by weight) paraffin or cetyl alcohol were quite paraffin oil coatings were and then coated with stable. Linseed oil and white also satisfactory. Synthetic plastic coatings would be effective although expensive.

The coated product is then bagged in heat-scalable polyethylene or other commercially available synthetic plastic fertilizer bags. A number of such plastics were tested; most are equal or superior to polyethylene but are generally more expensive or are not yet available as fertilizer ags. All of the equipment used in the steps above should The ammonia recovered from these units might be used by recycling to the precipitation step or to a downstream plant making some other material.

The combination of the .above steps makes it possible to use ammonium carbamate as a fertilizer material. Use of the plastic bags reduces loss during storage to a negligible amount. The combination of pressure pelletizing and oil coating reduces losses during open exposure to a 'In determining loss during open exposure, a test period of five hours was used. This should be adequate for a period between opening the bag on the farm and applying the material to the soil. It would be necessary to place the material beneath rather than on the surface of the soil. Light coverage, on the order of As in the case of aqua ammonia, volatilization loss is prevented by sorption of ammonia on soil particles.

It is necessary to use the particular combination .of steps, which have been described, to make the use of carbamate as a fertilizer feasible. Use of plastic bags to however, this alone would not be adequate for carbamate since loss after opening of the bag would be too great. Use of oily or waxy coatings is also known; however, this alone would not be adequate since loss during storage in pervious bags would be too large. The coated carbamate does decompose to a slight extent during bag storage. However, as soon as the atmosphere in the bag becomes saturated with ammonia, and pressure is equalized between the interior and exterior of the bag, little further loss takes place. The coating has no function during storage in the plastic bag; unconditioned carbamate would store as well. The function of the coating and the high particle density comes into effect only during bagging or when the bag is opened. It is probably possible to put on a coating that would permit the use of porous bags or the open storage of carbamate. However, such a coating would be too thick or too expensive to be practical. The only feasible approach is to control long-term storage loss by a suitable container and the short-term loss from exposed the particle density as described.

Control of the variables to give a particular combination is necessary for best results. As has been mentioned, the pellets should be large, preferably larger than 10 mesh. Best results were obtained at a particular pelletizing pressure, about 40,000 p.s.i.g. Unexpectedly, higher pressures gave a less stable product. A particular viscosity range of oil, about 200 to 215 Saybolt seconds at 130 F., was best; the reason for this is not readily evident. A combination of oil impregnation and a solid coating gave particularly good results. Presumably, the internal oil coating on the crystals making up the pellet slowed movement of ammonia to the surface, thus making the surface 'barrier more effective.

of ammonium carbamate from the precipitation of same by the reaction of anhydrous ammonia with carbon dioxide followed by compaction into pellets, which pellets in turn are subsequently coated, with or without prior impregnation thereof, and sent to storage in bags whose walls are impervious to ammonium vapor are given by way of illustration and not by way of limitation.

Example I Pellets of dry ammonium carbamate were made by compaction over the range of 20,000 to 100,000 p.s.i.g. (calculated from compactor area and load). Storage of the pellets for5 hours under humid conditions (79 percent relative humidity) at atmospheric pressure (standard decomposition test) indicated that a minimum decomposi- .tion loss of 15 percent by weight occurred with the pellets substrate was lost from the pellets having a 4.5 percent oil coating, as compared to 15 percent from uncoated pellets (Example 1).

Example III Pellets produced at 50,000 p.s.i.g. were coated with four petroleum oils of different viscosities, i.e., SAE-lO, -20, --30, and -40. The coatings were 5.5 percent by each case. The pellets coated with the medium Saybolt seconds at 130 F.) lost about 3 percent by weight; those coated with SAE-10 Saybolt seconds at F), SAE-20 (152 Saybolt seconds at 130 F.), and SAE-40 (270 Saybolt seconds at 130 F.) lost 5 to 6 weight percent in the standard exposure test.

Example IV Pellets produced at.40,000 p.s.i.g. were coated with a mixture of No.6 fuel oil (77.5 percent by'weight) and No. 1 diesel oil (22.5 percent by weight) such that the coating amounted to 3.5 percent by weight. The viscosity of this mixture was about 200 Saybolt seconds at 130 F. (slightly lower than that of SAE 30). Under the standard exposure test conditions, the pellets lost only 3 percent of their weight.

Example V Pellets produced at 40,000 p.s.i.g. pressure from oil (SAE20) soaked carbamate in such a way as to leave the pellets impregnated with the oil (about 2 percent by weight) were further spray coated with molten'p'araffin (3.5 percent) or molten cetyl alcohol (8 percent-a hy- Example VI Pellets produced in the usual manner were coated with a 6 percent coating of cottonseed oil; the pellets lost 1.0 percent by weight in the standard exposure test.

Example VII that the appended claims are intended to cover such modifications and variations that are within the true scope and spirit of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

11- A process for the production of a nitrogen-containing fertilizer material which comprises the steps of reacting anhydrous ammonia with carbon dioxide; collecting the resulting light crystalline ammonium carbamate material; compacting and pelletizing said resulting ammonium carbamate material; classifying by size said pelletized material and separating out therefrom those peldesired of a predetermined size; spray coating said sized ammonium carbamate pellets with a petroleum based oil of medium viscosity; coated ammonium walls of which are vapor.

and storing said spraycarbamate pellets in containers, the substantially impervious to ammonia wherein the :pelletizing pressure to which the light crystalline ammonium carbamate material is subjected is on the order of approximately 40,000 pounds per square inc 3. The process of claim 2 wherein the viscosity of the etroleum based oil used therein is in the range of about 200 to 215 Saybolt seconds at F.

4. The process of claim 3 wherein the material selected from said classifying step as onsize is in the mesh range from about 10 mesh up to about 6 mesh.

5. The process of claim 3 wherein the compacted pellets of ammonium carbamate are impregnated with from about 2 to about 3 percent by weight of a petroleum based oil prior to the spray coating of the sized pellets.

6. The process of claim 5 wherein the hydrophobic medium used to spray the liquid petroleum based oil impregnated ammonium carbamate pellets is selected from the group consisting of molten parafiln, molten cetyl alcohol, cottonseed oil, and mixtures thereof.

References Cited by the Examiner UNITED STATES PATENTS 3,048,478 8/1962 Smith 71-64 X 3,223,518 12/1965 Hansen 71-64 OTHER REFERENCES DONALL H. SYLVESTER, Primary Examiner. R. BAJEFSKY, Assistant Examiner. 

1. A PROCESS FOR THE PRODUCTION OF A NITROGEN-CONTAINING FERTILIZER MATERIAL WHICH COMPRISES THE STEPS OF REACTING ANHYDROUS AMMONIA WITH CARBON DIOXIDE; COLLECTING THE RESULTING LIGHT CRYSTALLINE AMMONIUM CARBAMATE MATERIAL; COMPACTING AND PELLETIZING SAID RESULTING AMMONIUM CARBAMATE MATERIAL; CLASSIFYING BY SIZE SAID PELLETIZED MATERIAL AND SEPARATING OUTTHEREFORM THOSE PELLETS DESIRED OF A PREDETERMINED SIZE; SPRAY COATING SAID SIZED AMMONIUM CARBAMATE PELLETS WITH A PETROLEUM BASED OIL OF MEDIUM VISCOSITY; AND STORING SAID SPRAYCOATED AMMONIUM CARBAMATE PELLETS IN CONTAINERS, THE WALLS OF WHICH ARE SUBSTANTIALLY IMPERVIOUS TO AMMONIA VAPOR. 